Family Study of Affective Disorders: The transmission of several affective illnesses in first degree relatives fits a multifactorial-inheritance model of a single underlying liability. Schizoaffective illness represents the most extreme liability, next is bipolar, and unipolar illness has the smallest genetic liability. Single-locus models do not fit these data. Dopamine-beta-hydroxylase in plasma is linked to ABO blood group locus on chromosome 9, but is unlinked to affective illness. A cell culture laboratory with a series of fibroblast cell lines from patients and relatives was established. The fibroblasts show specific binding suggestive of muscarinic cholinergic and beta-adrenergic receptors. Genetic variation in plasma methoxyhydroxyphenylglycol (MHPG), plasma gamma-hydroxy butyric acid-(GABA), platelet 3H-imipramine binding, and platelet GABA-transaminase, have been identified.